Lots of fixes importing SDL source wholesale into a new iOS project

--HG--
rename : src/libm/math.h => src/libm/math_libm.h

src/video/directfb/SDL_DirectFB_opengl.c

@@ -18,6 +18,9 @@
      misrepresented as being the original software.
   3. This notice may not be removed or altered from any source distribution.
 */
+#include "SDL_config.h"
+
+#if SDL_VIDEO_DRIVER_DIRECTFB
 
 #include "SDL_DirectFB_video.h"
 
@@ -352,4 +355,6 @@ DirectFB_GL_DestroyWindowContexts(_THIS, SDL_Window * window)
 
 #endif
 
+#endif /* SDL_VIDEO_DRIVER_DIRECTFB */
+
 /* vi: set ts=4 sw=4 expandtab: */